Cathode degradation in a field emission device (FED) is often caused by electron beam-induced desorption of gases from the anode of the device. These gases, along with other contaminating materials present in the FED, tend to settle on the surface of the microtips of the cathode during operation and manufacture of the FED, causing field emission from the cathode to degrade over time due to changes in the work function of the material comprising the microtips. The change in the fractional coverage of the microtips by contaminating impurities is a function of the pressure in the FED plus the arrival rate of contaminating impurities on the surface of the microtips minus the departure rate of contaminating impurities from the surface of the microtips.
Degradation in field emission in an FED over time may also be caused by the diffusion of contaminating impurities over the surface of the microtips of the FED. Field emission from an FED is aided if the microtips of the FED remain free of impurities during both manufacture and operation of the FED.